1. Field of the Invention
The present invention relates generally to internal combustion engines, and more particularly, to a misfire detection apparatus and method for an internal combustion engine.
2. Description of the Related Art
The Clean Air Act 1975 required motor vehicle manufacturers to reduce exhaust emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen from light duty motor vehicles. To comply with the Act, most motor vehicle manufacturers have used catalytic convertors on production motor vehicles to control such exhaust emissions.
Recently, regulatory agencies have proposed that passenger, light-duty and medium-duty motor vehicles with feedback fuel control systems be equipped with a malfunction indicator light that will inform the motor vehicle operator of any malfunction of an emission-related component that interfaces with an on-board computer of the motor vehicle. It is also proposed or required that an on-board diagnostic system identify the likely area of malfunction. Proposals or requirements have set forth catalyst, misfire, evaporative purge system, secondary air system, air conditioning system refrigerant, fuel system, oxygen sensor, exhaust gas recirculation, and comprehensive component monitoring requirements.
Misfire of internal combustion engines can damage the catalyst of a catalytic convertor. With respect to misfire, the identification of the specific cylinder experiencing misfire may be required. Some regulations provide that the motor vehicle manufacturer specify a percentage of misfires out of the total number of firing events necessary for determining malfunction for: (1) the percent misfire evaluated in a fixed number of revolution increments for each engine speed and load condition which would result in catalyst damage; (2) the percent misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail a Federal Test Procedure (FTP) by more than 150% of the applicable standard if the degree of misfire were present from the beginning of the test; and (3) the degree of misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail an Inspection and Maintenance (IM) program tailpipe exhaust emission test.